Evaluation of set-up reproducibility with and without customized vacuum immobilization device in rectal cancer patients treated with preoperative pelvic radiation therapy

Hdl Handle:
http://hdl.handle.net/10147/239013
Title:
Evaluation of set-up reproducibility with and without customized vacuum immobilization device in rectal cancer patients treated with preoperative pelvic radiation therapy
Citation:
International Journal of Radiation Oncology Biology Physics (2011) 81:2 SUPPL. 1 (S171-S172). : 1 Oct 2011
Journal:
International Journal of Radiation Oncology Biology Physics
Issue Date:
Oct-2011
URI:
http://hdl.handle.net/10147/239013
Abstract:
Purpose/Objective(s): Image-guided radiation therapy (IGRT) allows accurate patient (pt) set-up prior to initiating treatment. It is unclear if this increased accuracy eliminates the need for custom vacuum immobilization devices (CVID), or if they provide patient positioning benefits in conjunction with IGRT. A randomized study was conducted to assess whether intrafractional uncertainty without CVID is comparable to the use of a CVID for preoperative pelvic radiation therapy (preop-RT) for rectal cancer pts. Materials/Methods: Rectal cancer pts who were recommended to undergo preop-RT were consented and randomized to either initial treatment with CVID or without (prone pillow under the head and upper thorax and ankle fixation device). After 13 of 25 fractions, each pt was switched to the alternative positioning method. Two treatment plans were generated (with and without the CVID) for each pt. Pts were treated prone. Daily CBCT scans were performed before (pretreatment localization) and after (to quantify intrafractional movement) each fraction. All data was re-analyzed offline. Intrafractional systematic and random errors were calculated for comparison. The F-test was used to test for significant differences in variance between groups. Results: From April 09 - June 10, 20 pts were enrolled (9 female; 11 male; median age 58; median BMI 27.2; 3 stage I (15%), 6 stage II (30%), 9 stage III (45%) and 2 stage IV (10%)). Intrafractional motion was assessed in left-right (LR), superior-inferior (SI) and anterior-posterior (AP) directions. For pts in CVID, systematic uncertainty was 0.3mm LR, 0.7mm SI and 0.7mm AP, while random uncertainty was 1.0mm LR, 1.3mm SI and 1.5mm AP. For pts without CVID, systematic uncertainty was 1.8mm LR, 0.7mm SI and 1.0mm AP, while random uncertainty was 2.1mm LR, 1.2mm SI and 1.5mm AP. No statistical significance was noted in the shifts in AP and SI directions. The difference in systematic and random LR intrafractional uncertainties was clinically small but statistically significant (p<0.00001). The difference in LR intrafractional uncertainty (+/- CVID) remained when pts were analyzed by gender, BMI and initial pre-correction position on univariate analysis. Conclusions: For rectal cancer pts undergoing preop-RT in the prone position localized with daily CBCT, CVID provides a statistical improvement in pt intrafractional lateral stability compared to a simpler set-up. However, the 1.5mm magnitude of this improvement is small and should be considered in the context of the other uncertainties. A simple set-up without CVID is clinically appropriate for pelvic IMRT if the LR displacement is accounted for in PTV margins.
Item Type:
Conference Presentation
Language:
en
Keywords:
RADIATION; THERAPY; CANCER

Full metadata record

DC FieldValue Language
dc.date.accessioned2012-08-16T15:10:04Z-
dc.date.available2012-08-16T15:10:04Z-
dc.date.issued2011-10-
dc.identifier.citationInternational Journal of Radiation Oncology Biology Physics (2011) 81:2 SUPPL. 1 (S171-S172). : 1 Oct 2011en_GB
dc.identifier.urihttp://hdl.handle.net/10147/239013-
dc.description.abstractPurpose/Objective(s): Image-guided radiation therapy (IGRT) allows accurate patient (pt) set-up prior to initiating treatment. It is unclear if this increased accuracy eliminates the need for custom vacuum immobilization devices (CVID), or if they provide patient positioning benefits in conjunction with IGRT. A randomized study was conducted to assess whether intrafractional uncertainty without CVID is comparable to the use of a CVID for preoperative pelvic radiation therapy (preop-RT) for rectal cancer pts. Materials/Methods: Rectal cancer pts who were recommended to undergo preop-RT were consented and randomized to either initial treatment with CVID or without (prone pillow under the head and upper thorax and ankle fixation device). After 13 of 25 fractions, each pt was switched to the alternative positioning method. Two treatment plans were generated (with and without the CVID) for each pt. Pts were treated prone. Daily CBCT scans were performed before (pretreatment localization) and after (to quantify intrafractional movement) each fraction. All data was re-analyzed offline. Intrafractional systematic and random errors were calculated for comparison. The F-test was used to test for significant differences in variance between groups. Results: From April 09 - June 10, 20 pts were enrolled (9 female; 11 male; median age 58; median BMI 27.2; 3 stage I (15%), 6 stage II (30%), 9 stage III (45%) and 2 stage IV (10%)). Intrafractional motion was assessed in left-right (LR), superior-inferior (SI) and anterior-posterior (AP) directions. For pts in CVID, systematic uncertainty was 0.3mm LR, 0.7mm SI and 0.7mm AP, while random uncertainty was 1.0mm LR, 1.3mm SI and 1.5mm AP. For pts without CVID, systematic uncertainty was 1.8mm LR, 0.7mm SI and 1.0mm AP, while random uncertainty was 2.1mm LR, 1.2mm SI and 1.5mm AP. No statistical significance was noted in the shifts in AP and SI directions. The difference in systematic and random LR intrafractional uncertainties was clinically small but statistically significant (p<0.00001). The difference in LR intrafractional uncertainty (+/- CVID) remained when pts were analyzed by gender, BMI and initial pre-correction position on univariate analysis. Conclusions: For rectal cancer pts undergoing preop-RT in the prone position localized with daily CBCT, CVID provides a statistical improvement in pt intrafractional lateral stability compared to a simpler set-up. However, the 1.5mm magnitude of this improvement is small and should be considered in the context of the other uncertainties. A simple set-up without CVID is clinically appropriate for pelvic IMRT if the LR displacement is accounted for in PTV margins.en_GB
dc.language.isoenen
dc.subjectRADIATIONen_GB
dc.subjectTHERAPYen_GB
dc.subjectCANCERen_GB
dc.titleEvaluation of set-up reproducibility with and without customized vacuum immobilization device in rectal cancer patients treated with preoperative pelvic radiation therapyen_GB
dc.typeConference Presentationen
dc.identifier.journalInternational Journal of Radiation Oncology Biology Physicsen_GB
dc.description.provinceLeinsteren
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